Neutral gray absorbing glass comprising manganese oxide for selenium retention during processing

ABSTRACT

A neutral gray, heat absorbing soda-lime-silica glass having at 4 mm. control thickness a light transmittance using illuminant A of 10.0% to 55.0%, ultra violet transmittance less than 25.0%, and infra red transmittance is less than about 50.0% produced with colorants consisting of 0.90 to 1.90 percent by weight total iron oxide as Fe 2  O 3 , 0.002 to 0.025 percent Co, 0.0010 to 0.0060 percent Se, 0.10 to 1.0 percent MnO 2 , and 0 to 1.0 percent TiO 2 . The flat glass products having such a composition is particularly suitable for use as a privacy glass or sun roof product in trucks and automobiles.

BACKGROUND OF THE INVENTION

This invention is directed to a heat absorbing, neutral gray coloredglass composition. More particularly, it comprises soda-lime-silicaglass whose coloring components consist essentially of iron oxide,cobalt, selenium, manganese dioxide, and optionally titanium dioxide.

Glass having a neutral gray color and properties such as low infra redtransmittance and low total solar energy transmittance which reduce theheat gain in the interior of an enclosure is highly desired in theautomotive field. The neutral gray color is chosen for the sake ofcoordinating with a wide range of automotive paint colors. To beparticularly useful in the automotive field, the glass compositionshould be one that is compatible with flat glass manufacturing methods.A glass composition having these properties would be highly desirable,particularly for automotive privacy and sun roof applications.

Some other heat absorbing gray glass compositions contain selenium as anessential coloring component. For example, U.S. Pat. No. 4,873,206 toJones discloses a gray glass composition which includes as the colorantsonly iron, cobalt, and selenium. Selenium is a relatively low meltingcomponent with a melting point of 217° C. and a boiling point of 685° C.which typically leads to a volatilization of 85% or more of the seleniumfrom the glass batch during glass melting and processing. Selenium is avery expensive material and hence its emission during glass melting isless than desirable. This high level of volatilization takes place eventhough glass manufacturers typically use sodium or potassium nitrates inthe glass composition in an attempt to retain more of the selenium inthe glass product.

The present invention overcomes problems associated with seleniumvaporization by incorporating manganese oxide into a grey glasscomposition along with the selenium. We have unexpectedly found thatincorporating the manganese oxide into a selenium containing glasscomposition aids in selenium retention during melt processing.

In addition, contrary to the suggestion of Jones in the patent listedabove, including manganese oxide in the present invention compositionalong with the iron oxide did not lead to increased solarization.Solarization is the result of reactions that occur in glass when exposedto UV radiation such as that in sunlight. One such reaction is the shiftof Fe⁺³ towards Fe⁺². Solarization causes the iron to move from theoxidized species to the reduced species which also causes an undesirablecolor shift in the glass product. This problem of solarization is alsodiscussed by Milos B. Volf in Chemical Approach to Glass, ElsevierScience Publishing Co., Inc., 1984, p. 343. "Manganese as a decolorizerhas the disadvantage of creating solarization and of being sensitive tothe furnace atmosphere."

Generally, gray colored heat absorbing glasses relied, in the past, onthe inclusion of nickel oxide as an active coloring agent. Nickelcompounds, however, are known to react with other materials insoda-lime-silica glass and form nickel sulfide "stones" in the glass.These stones are usually small, thereby avoiding detection methods, butcan produce an unacceptably high rate of breakage during tempering ofthe glass. U.S. Pat. No. 5,023,210 to Krumwiede et al. discloses the useof chrome oxide in combination with iron oxide, cobalt oxide andselenium to achieve a dark gray glass without nickel. It does notinclude MnO₂.

SUMMARY OF THE INVENTION

The present invention is a soda-lime-silica glass composition that isheat absorbing with a neutral gray color and improved seleniumretention. The composition in its broadest embodiment comprises 68 to75% SiO₂, 10 to 18% Na₂ O, 5 to 15% CaO, 0 to 10% MgO, 0 to 5% Al₂ O₃,and 0 to 5% K₂ O, where CaO + MgO is 6 to 15% and Na₂ O +K₂ O is 10 to20%, with traces of melting and refining aids, if any, and colorantsconsisting essentially of: 0.90 to 1.90 wt. % total iron oxide as Fe₂ O₃; 0.002 to 0,025 wt. % cobalt as Co; 0.0010 to 0.0060 wt. % selenium asSe; 0.10 to 1.0 wt. % manganese oxide as MnO₂ ; and 0.0 to 10% titaniumoxide as TiO₂.

Glass products made according to embodiments of the invention have thefollowing spectral properties at 4 mm thickness: 10.0 to 55.0% lighttransmittance using illuminant A (LTA), less than 25.0% ultra violettransmittance, and less than 50.0% infra red transmittance. Preferably,the composition has a dominant wavelength between about 470 and 590nanometers. Generally, as the quantities of the colorants increase, the% transmittance will go down. Similarly, generally as the glassthickness increases for a given glass composition, the transmittance ofthe thicker glass will decrease.

We have unexpectedly discovered that introducing manganese oxide in thebatch increases the retention of selenium in the glass product over andabove that obtained by incorporating nitrates. While the major functionof the manganese oxide is to increase the selenium retention, there issome absorption by manganese oxide in the same portion of the visiblespectrum as the selenium component, hence incorporation of manganeseoxide also further enhances the grey color. Thus, less of the costlyselenium is necessary to be present in the composition since themanganese oxide in effect also acts to provide the grey color.Desirably, the glass composition of this invention has a gray colorwhich is obtained without the addition of nickel.

DETAILED DESCRIPTION OF THE INVENTION

Flat soda-lime-silica glass, used in the automotive and architecturalindustries and conveniently made by the float glass process, isgenerally characterized by the following basic composition shown inTable I, the amounts of the components being based on a weightpercentage of the total glass composition:

                  TABLE I                                                         ______________________________________                                        Oxide Component  Weight %                                                     ______________________________________                                        SiO.sub.2        68 to 75                                                     Al.sub.2 O.sub.3 0 to 5                                                       CaO               5 to 15                                                     MgO               0 to 10                                                     Na.sub.2 O       10 to 18                                                     K.sub.2 O        0 to 5                                                       ______________________________________                                    

The neutral gray glass composition of the present invention employs thisbasic soda-lime-silica glass composition wherein, additionally, CaO +MgO is 6 to 15% and Na₂ O + K₂ O is 10 to 20%. Preferably SO₃ is 0.10 to0.30 wt. %, more preferably 0.14 to 0.25 wt. %. In addition, the neutralgray glass composition consists essentially of the following coloringcomponents: iron oxide; cobalt oxide; selenium; manganese oxide; andoptionally titanium dioxide as summarized above.

The total iron oxide as Fe₂ O₃ is present in the invention compositionin quantities of 0.9 to 1.90 weight %. All weight percents disclosedherein are based on the total weight of the invention glass composition.Typically, this ingredient is added into the batch ingredients in oxideform, e.g., Fe₂ O₃. The iron oxide incorporated in the compositionlowers both the ultra violet and the infra red transmittance of theglass products. More particularly, the iron oxide performs two functionsin this glass system: (1) the oxidized form of iron oxide (Fe₂ O₃)absorbs in the ultra violet portion of the spectrum providing low ultraviolet transmittance, and (2) the reduced form of iron oxide (FeO)absorbs in the infra red portion of the spectrum and the resultant glassthus has a lowered infra red transmittance. Both absorbing functions ofthe iron oxide are especially valuable when the glass product is used inautomobiles. When heat is absorbed by the glass, the load on airconditioners is initially reduced and there is less total heat in thevehicle to cool.

Cobalt, which is typically added to the batch ingredients as an oxidethereof, is present as a coloring component in the invention glasscomposition in an amount of 0,002 to 0,025 wt. % as Co, the cobaltfunctioning to absorb light from about 580 to 680 nanometers in thevisible portion of the spectrum. Selenium, which is typically added tothe batch ingredients as a metal, is present as a coloring component inan amount of 0.0010 to 0.0060 wt. % Se, the selenium functioning toabsorb light from about 430 to 540 nanometers of the visible spectrum.It is necessary to balance the amount of absorption from selenium withthat of cobalt to achieve a neutral gray appearance.

Manganese oxide is present in the grey glass invention composition in anamount of 0.10 to 1.0 wt % based on MnO₂. Manganese oxide can be addedto the batch glass components in a variety of forms, e.g., MnO₂, MnO₄,MnO, etc. In the glass composition, it is generally present in the Mn⁺²and Mn⁺³ state, although it may additionally be present in other statessuch as Mn⁺⁴. There are two functions that manganese oxide performs inthe present invention composition: (1) one form of manganese in theglass absorbs in the same area as selenium so that it replaces a portionof the selenium, and (2) manganese oxide acts as an oxidizer and helpsto retain a larger proportion of selenium from the batch. Typically, incompositions without manganese oxide, a large amount of selenium (about85-90%) which is very costly volatilizes from the batch even when usingsodium or potassium nitrates as oxidizers. Therefore, our finding thatmanganese oxide is extremely beneficial in retaining a higher proportionin the final glass product of the selenium added into the batch (˜300%increased selenium retention) was unexpected and is a critical point ofthis invention. As discussed above and in more detail below,unexpectedly we have also found that contrary to prior teachings,including manganese oxide along with iron oxide in the glass compositiondid not cause any appreciable solarization (discoloring) after exposureto ultra-violet light. We have discovered that employing manganese oxidealong with iron oxide in amounts as specified in this inventioncomposition, allows the solarization phenomena to be minimized.

Titanium dioxide may optionally be used in the present invention neutralgray glass composition to enhance achievement of a particular range ofdominant wavelength to the glass composition. Gray glasses of thisinvention are preferably those with an excitation purity of less thanabout 5.5%. It is important that the present invention glass product bea neutral gray, more specifically being a green gray; preferably thedominant wavelength with illuminant C is between 470 and 590 nanometers(nm), more preferably between 480 and 570 nm, most preferably between487.5 and 558 nm, using the C.I.E. convention with a 2° observer.Titanium dioxide is very useful in shifting the dominant wavelengthwithin the range of 470 to 590 nanometers. Titanium dioxide also absorbsin the ultra violet range of the spectral curve and helps to lower theultra violet transmittance of glass in this invention.

We have found that glasses within the broadest scope of this inventionhave the following spectral properties when measured at a controlthickness of 4.0 millimeters: light transmittance with illuminant A(LTA) between 10.0% and 55.0%, ultra violet transmittance of less than25.0%, preferably less than about 10.0% when the glass has less than35.0% LTA, and infra red transmittance is less than about 50.0%. Aswould be apparent to those skilled in the art in view of the presentdisclosure, the glass composition of this invention may also be madeinto glass at other thicknesses. Generally, although not meant to be solimited, the thickness for the glass product would be within the rangeof 2.0 to 12.0 millimeters which is typical of glass produced by thefloat process.

Table II discloses the amounts of raw material batch ingredients whichare preferably used to form embodiments of neutral gray glasscompositions according to the present invention.

                  TABLE II                                                        ______________________________________                                        BATCH MATERIAL  RANGE MASS (LBS.)                                             ______________________________________                                        Sand            1000                                                          Soda Ash        290 to 320                                                    Dolomite        215 to 260                                                    Limestone       75 to 90                                                      Salt Cake        6 to 24                                                      Rouge (97% Fe.sub.2 O.sub.3)                                                                  17 to 23                                                      Titanium Dioxide                                                                              0 to 5                                                        Sodium Nitrate   3 to 20                                                      Manganese Dioxide                                                                             2 to 8                                                        Carbocite (70% C)                                                                             0.1 to 1.5                                                    Cobalt Oxide (Co.sub.3 O.sub.4)                                                               0.30 to 0.36                                                  Selenium        0.20 to 0.70                                                  ______________________________________                                    

As would be appreciated by those skilled in the art, processing aids aregenerally added to the glass batch during the melting and processing,e.g., to maintain the proper balance of redox conditions or as finingagents. For example, carbocite (anthracite coal) when added to the glasscomposition has the effect of reducing a portion of the Fe₂ O₃ to FeO toachieve lower infra red transmittance. Sodium and/or potassium nitrateare used in glass batches of the invention to maintain oxidizingconditions early in the melting process which aids in seleniumretention. Nitrates have been used by others to improve seleniumretention. Careful balance must be maintained between the reducingconditions from the carbocite and the oxidizing conditions from thenitrates and manganese dioxide used to improve selenium retention in theglass, because the oxidizers also act upon the iron oxide to shift theredox from FeO toward Fe₂ O₃ while carbocite shifts the iron oxideequilibrium in the opposite direction. As disclosed above, we havediscovered that employing manganese oxide along with iron oxide in theamounts specified for the invention composition, allows the solarizationphenomena to be minimized. The quantities of salt cake, carbocite andsodium nitrate preferably used in the batch ingredients to achieve thedesired ratio between the two iron oxides in the final composition alsohelps to retard solarization in the invention glass. More preferably,the lbs. of batch materials: salt cake; sodium nitrate; carbocite is8-18; 5-15; 0.3-1.0, and most preferably are: 8-12; 5-10; 0.3-1.0,respectively per 1000 lbs. of sand. These disclosed most preferredamounts of the three batch materials is associated with a final glassproduct preferably having 0.15-0.60 wt. % MnO₂ and 1.2-1.6 wt.% totaliron as Fe₂ O₃ in the final glass composition.

In order to show the unexpected effects of manganese dioxide onimproving selenium retention in our glass composition, eight grey glasscompositions were made as described below in Tables III and IV. Neutralgray glass compositions made according to embodiments of this inventionwere detailed as Examples 1-4. For comparison, similar glasscompositions except without manganese dioxide were made as detailed asExamples 5-8. All of these glasses were made by the following procedure.The batches were weighed (typically 170 grams total) on a laboratorybalance and mixed within a glass jar for 10 minutes each using alaboratory shaker. Each mixed batch was placed into a platinum-rhodiumcrucible which was about 2" tall with about a 2.5" inside diameter and4.5 ml. of water was mechanically mixed into the raw batch. Crucibleswere placed into a natural gas/air furnace pre-heated to 2600° F. with 3to 5 other crucibles. Furnace temperature recovers to 2600° F. in about30 minutes. After two hours melting, each crucible was removed in turn,glass in the crucible was fritted by quenching in cold water, and thefragments were mixed in the crucible and all crucibles were returned tothe furnace. Furnace temperature was brought back to 2600° F. and thefritting procedure was repeated as in the step above once the operatingtemperature was attained, about 45 minutes. All glass samples weremelted for another 3 hours and each sample was poured into a 2.5" insidediameter graphite mold to shape the glass samples for subsequentgrinding and polishing. All samples were placed into an annealingfurnace, brought up to 1050° F., held for 4 hours, then allowed toslowly cool to room temperature in about 16 hours. Samples were groundand polished and spectral properties were measured on each sample;spectral properties were calibrated to a control thickness of 4 mm.Samples were then chemically analyzed via X-ray fluorescence or othertests conducted as needed.

                  TABLE III                                                       ______________________________________                                                   Example                                                                              Example  Example  Example                                              1      2        3        4                                         ______________________________________                                        Sand         100.00   100.00   100.00 100.00                                  Soda Ash     31.41    31.41    31.41  31.41                                   Limestone    7.25     7.25     7.25   7.25                                    Dolomite     25.83    25.83    25.83  25.83                                   Salt Cake    1.0956   1.0960   1.0969 1.0969                                  Sodium Nitrate                                                                             0.5215   0.5192   0.5233 0.5236                                  Rouge        1.8133   2.1103   1.9683 2.1061                                  Carbocite    0.0916   0.0914   0.0916 0.0907                                  Cobalt Oxide 0.0142   0.0313   0.0370 0.0392                                  Manganese Dioxide                                                                          0.5304   0.8107   1.3750 0.5315                                  Selenium     0.0209   0.0490   0.0430 0.0577                                  ppm Selenium 26       75       70     80                                      in Glass                                                                      % Selenium Retained                                                                        17.1     21.0     22.3   19.0                                    ______________________________________                                    

Present invention compositions of Examples 1-4 show amounts of retainedselenium of between 17.1 and 22.3%. In contrast, comparative Examples5-8 below, not according to this invention (i.e., not including MnO₂)show amounts of retained selenium of only between 6.2 and 7.8%. Theseexamples show an almost 300% increase in selenium retention whenmanganese dioxide is employed along with the selenium as in the presentinvention compositions.

                  TABLE IV                                                        ______________________________________                                                   Example                                                                              Example  Example  Example                                              5      6        7        8                                         ______________________________________                                        Sand         100.00   100.00   100.00 100.00                                  Soda Ash     31.41    31.41    31.41  31.41                                   Limestone    7.25     7.25     7.25   7.25                                    Dolomite     25.83    25.83    25.83  25.83                                   Salt Cake    1.0961   1.0960   1.0960 1.0958                                  Sodium Nitrate                                                                             0.5187   0.5234   0.5220 0.5188                                  Rouge        2.1078   1.8144   2.1105 2.1051                                  Carbocite    0.0912   0.0913   0.0912 0.0917                                  Cobalt Oxide 0.0165   0.0144   0.0317 0.0389                                  Selenium     0.0286   0.0414   0.0963 0.1116                                  ppm Selenium 8        10       22     28                                      in Glass                                                                      % Selenium Retained                                                                        7.8      6.5      6.2    6.2                                     ______________________________________                                    

Table V below lists the preferred ranges of resultant oxide constituentsof our new glass composition. Following the table are the spectralproperties of such preferred glass compositions according to theinvention.

                  TABLE V                                                         ______________________________________                                        Oxide Component Weight %                                                      ______________________________________                                        SiO.sub.2       71 to 74                                                      Al.sub.2 O.sub.3                                                                              0.15 to 0.25                                                  Fe.sub.2 O.sub.3                                                                              1.20 to 1.60                                                  CaO             8.40 to 8.70                                                  MgO              3.5 to 4.00                                                  Na.sub.2 O      13.00 to 13.80                                                K.sub.2 O         0 to 0.10                                                   TiO.sub.2       0.00 to 0.35                                                  MnO.sub.2       0.15 to 0.6                                                   SO.sub.3        0.14 to 0.25                                                  Co (metal)      0.0160 to 0.0185                                              Se (metal)      0.0020 to 0.0040                                              Preferred Glass Property Ranges (4 mm. thick glass sheet)                     Visible Transmission (Ill. A):                                                                       16-20%                                                 Ultraviolet Transmission:                                                                             5-10%                                                 Infrared Transmission: 10-18%                                                 Total Solar Transmission:                                                                            12-20%                                                 Dominant Wavelength:   .sub.  470-590 nm                                      Excitation Purity:     0.0-5.5%                                               FeO/Total Iron Oxide as Fe.sub.2 O.sub.3 Ratio:                                                      0.18-0.26                                              ______________________________________                                    

Examples of the amounts of raw materials used to make various preferredembodiments of neutral gray glass compositions according to the presentinvention were set out in Table VI below. The table also details thespectral properties of the resulting glasses:

                  TABLE VI                                                        ______________________________________                                        Example      Example  Example  Example                                                                              Example                                 9            10       11       12     13                                      ______________________________________                                        Sand    100.00   100.00   100.00 100.00 100.00                                Soda Ash                                                                              31.41    31.41    31.41  31.41  31.41                                 Limestone                                                                             7.25     7.25     7.25   7.25   7.25                                  Dolomite                                                                              25.83    25.83    25.83  25.83  25.83                                 Salt Cake                                                                             1.0966   1.0959   1.0960 1.0960 1.0961                                Sodium  0.5198   0.5200   0.5205 0.5207 0.5204                                Nitrate                                                                       Rouge   2.0996   2.1008   2.1012 2.1010 2.1142                                Carbocite                                                                             0.0913   0.0910   0.0915 0.0914 0.0913                                Cobalt  0.0300   0.0308   0.0298 0.0305 0.0305                                Oxide                                                                         Manganese                                                                             0.1384   0.2705   0.2800 0.2802 0.5601                                Dioxide                                                                       Selenium                                                                              0.0550   0.0411   0.0418 0.0415 0.0281                                Titanium                                                                              0.0      0.0      0.0    0.0    0.5601                                Dioxide                                                                       % LTA   18.3     18.8     17.9   19.8   19.5                                  % UV    7.5      7.4      6.6    8.2    6.0                                   % IR    15.7     15.6     15.2   15.0   13.1                                  % TSET  16.7     16.8     16.1   16.9   15.5                                  Dominant                                                                              559.8    514.3    463.7  493.9  505.5                                 Wave-                                                                         length                                                                        Excitation                                                                            3.3      1.3      5.1    3.8    3.2                                   Purity, %                                                                     ______________________________________                                    

As used throughout the disclosure of this invention and in Table VIabove, % LTA is defined to be the % luminous transmittance measuredunder CIE standard illuminant A. As used herein, the % UV is the % ultraviolet transmittance as measured between 280 and 400 nanometers whilethe % IR is the % infra red transmittance measured over the range of 720to 2120 nanometers. The % TSET is the % total solar energy transmittanceas defined in U.S. Pat. No. 4 792 536 by the equation:

    % TSET=0.44% LTA+0.53% IR+0.03% UV

The dominant wavelength and % excitation purity are measured using CIEstandard illuminant C.

As discussed herein, glasses containing manganese and iron oxides havebeen known to solarize or discolor when exposed to a strong ultra violetlight source. For example, the Jones patent discussed above teaches thatglass containing iron oxide and MnO₂ is undesirable because the MnO₂causes a brown coloration after UV exposure. In contrast, the glasses ofthe present invention having the particular set of redox conditionswithin the scope of this invention, and specifically disclosed in detailabove, have been found not to experience any appreciable solarization.Table VII below shows this. Embodiments of the invention glass accordingto this invention exhibit only a modest change of the color after anaccelerated 3 month exposure in an Atlas, Model Ci65 Weather-ometerusing a Xenon UV lamp. This 3 month exposure in the Atlas Weather-ometeris considered equivalent to over 4 years exposure to the sun in Arizona.

                  TABLE VII                                                       ______________________________________                                                           Exposed 3                                                            Original Months     Difference                                      ______________________________________                                        Example 14--lab                                                                           Dominant   Dominant   +0.2                                        melt--no Mn nor Ti                                                                        Wavelength Wavelength                                                         483.0      483.2                                                  Example 15--lab                                                                           Dominant   Dominant   +1.0                                        melt--0.2% TiO.sub.2                                                                      Wavelength Wavelength                                                         493.2      494.2                                                  Example 16--lab                                                                           Dominant   Dominant   +1.6                                        melt--0.2% MnO.sub.2                                                                      Wavelength Wavelength                                                         568.6      570.2                                                  Example 17--lab                                                                           Dominant   Dominant   +1.4                                        melt--0.4% MnO.sub.2                                                                      Wavelength Wavelength                                                         557.0      558.4                                                  Example 14--lab                                                                           % Excitation                                                                             % Excitation                                                                             -0.3                                        melt--no Mn nor Ti                                                                        Purity 5.7 Purity 5.4                                             Example 15--lab                                                                           % Excitation                                                                             % Excitation                                                                             -0.3                                        melt--0.2% TiO.sub.2                                                                      Purity 2.9 Purity 2.6                                             Example 16--lab                                                                           % Excitation                                                                             % Excitation                                                                             +0.6                                        melt--0.2% MnO.sub.2                                                                      Purity 5.1 Purity 5.7                                             Example 17--lab                                                                           % Excitation                                                                             % Excitation                                                                              0.0                                        melt--0.4% MnO.sub.2                                                                      Purity 3.9 Purity 3.9                                             ______________________________________                                    

The scope of this invention includes not only glasses with lowtransmittance but other glasses that have a relatively high LTA whichare heat absorbing and have a neutral gray green color. Exemplary ofsuch glasses are those detailed in examples 18 and 19 in Table VIIIbelow:

                  TABLE VIII                                                      ______________________________________                                                       Example 18                                                                            Example 19                                             ______________________________________                                        Sand             100.00    100.00                                             Soda Ash         31.41     31.41                                              Limestone        7.25      7.25                                               Dolomite         25.83     25.83                                              Salt Cake        1.0960    1.0961                                             Sodium Nitrate   0.5204    0.5205                                             Rouge            1.3630    1.3630                                             Carbocite        0.0912    0.0913                                             Cobalt Oxide     0.0057    0.0095                                             Manganese Dioxide                                                                              0.2779    0.2779                                             Selenium         0.0280    0.0210                                             % LTA            53.2      48.7                                               % UV             23.9      23.4                                               % IR             26.4      26.6                                               % TSET           36.0      34.8                                               Dominant Wavelength                                                                            554.5     512.1                                              Excitation Purity, %                                                                           4.3       1.8                                                ______________________________________                                    

Table VIII above demonstrates glasses made within the scope of thisinvention which shows the sensitivity of the balance that must bemaintained between the cobalt and the selenium. A small increase incobalt and less selenium moves the dominant wavelength of Example 18toward a green color as in Example 19; the excitation purity also islowered from the cobalt and selenium adjustments made in Example 18 toExample 19.

We claim:
 1. A heat absorbing, neutral gray colored glass compositionhaving a base glass composition comprising by weight: 68 to 75% SiO₂, 10to 18% Na₂ O, 5 to 15% CaO, 0 to 10% MgO, 0 to 5% Al₂ O₃, and 0 to 5% K₂O, where CaO + MgO is 6 to 15% and Na₂ O + K₂ O is 10 to 20%, andcolorants consisting essentially of: 0.90 to 1.90 wt. % total iron oxideas Fe₂ O₃ ; 0.002 to 0.025 wt. % cobalt as Co; 0.0010 to 0.0060 wt. %selenium as Se; 0.10 to 1.0 wt. % manganese oxide as MnO₂ ; and 0.0 to1.0% titanium oxide as TiO₂ ; the glass at 4 mm. control thicknesshaving light transmittance using illuminant A of 10.0% to 55.0%, ultraviolet transmittance less than 25.0%, and infra red transmittance isless than about 50.0%.
 2. The neutral grey glass composition accordingto claim 1, wherein the dominant wavelength is between 470 and 590nanometers.
 3. The neutral grey glass composition according to claim 1,wherein SO₃ is present in the composition in an amount about 0.01 to0.03 wt. %.
 4. A heat absorbing, neutral gray colored glass compositionhaving a base glass composition comprising: 71 to 74% SiO₂, 13 to 13.80%Na₂ O, 8.4 to 8.7% CaO, 3.5 to 4% MgO, 0.15 to 0.25% Al₂ O₃, and 0 to0.1% K₂ O, where CaO + MgO is 6 to 15% and Na₂ O +K₂ O is 10 to 20%, andcolorants consisting essentially of: 1.20 to 1.60 wt. % total iron oxideas Fe₂ O₃ ; 0.0160 to 0.0185 wt. % cobalt as Co; 0.0020 to 0.0040 wt %selenium as Se; 0.15 to 0.60 wt. % manganese oxide as MnO₂ ; and 0.0 to0.35 wt. % titanium oxide as TiO₂, the glass at 4 mm. control thicknesshaving light transmittance using illuminant A between 16.0% and 20.0%,ultra violet transmittance between 5 and 10%, infra red transmittancebetween 10 and 18%, and a dominant wavelength between about 470 and 590nanometers.
 5. The neutral grey glass composition according to claim 4,wherein its excitation purity is less than about 5.5%.
 6. The neutralgrey glass composition according to claim 3, wherein the FeO/total ironoxide as Fe₂ O₃ is between 0.18 and 0.26.
 7. The neutral grey glasscomposition according to claim 1, wherein based on 1000 lbs. of sandused in batch ingredients to make said composition, other batchingredients comprise: 6-24 lbs. salt cake; 3-20 lbs. sodium nitrate; and0.1-1.5 lbs. carbocite.
 8. The neutral grey glass composition accordingto claim 6, wherein said batch ingredients comprise 8-18 lbs. salt cake;5-15 lbs. sodium nitrate; and 0.3-1.0 lbs carbocite.
 9. The neutral greyglass composition according to claim 8, wherein said batch ingredientscomprise 8-12 lbs. salt cake; 5-10 lbs. sodium nitrate; 0.3-1.0 lbs.carbocite; and said neutral grey glass composition comprises 0.15-0.60MnO₂ and 1.2-1.6 wt. % total iron as Fe₂ O₃.
 10. A heat absorbing,neutral gray colored glass composition having a base glass compositioncomprising by weight: 68 to 75% SiO₂, 10 to 18% Na₂ O, 5 to 15% CaO, 0to 10% MgO, 0 to 5% Al₂ O₃, and 0 to 5% K₂ O, where CaO + MgO is 6 to15% and Na₂ O + K₂ O is 10 to 20%, and colorants consisting essentiallyof: 0.90 to 1.90 wt. % total iron oxide as Fe₂ O₃ ; 0.002 to 0.025 wt. %cobalt as Co; 0.0010 to 0.0060 wt. % selenium as Se; 0.10 to 1.0 wt. %manganese oxide as MnO₂ ; and 0.0 to 1.0% titanium oxide as TiO₂ ; theglass at 4 mm. control thickness having light transmittance usingilluminant A of 10.0% to 55.0%, ultra violet transmittance less than25.0%, and infra red transmittance is less than about 50.0%; and beingmade from batch materials comprising sand, soda ash, dolomite,limestone, salt cake, rouge, sodium nitrate, a manganese containingcompound, carbocite, a cobalt containing compound, and selenium.
 11. Theneutral grey glass composition according to claim 10, wherein based on1000 lbs. of said sand in said batch ingredients used to make saidcomposition, said ingredients comprise 6-24 lbs. salt cake; 3-20 lbs.sodium nitrate; and 0.1-1.5 lbs carbocite.
 12. The neutral grey glasscomposition according to claim 11, wherein said ingredients comprise8-18 lbs. salt cake; 5-15 lbs. sodium nitrate; and 0.3-1.0 lbs.carbocite.
 13. The neutral grey glass composition according to claim 12,wherein said ingredients comprise 8-12 lbs. salt cake; 5-10 lbs. sodiumnitrate; 0.3-1.0 lbs. carbocite; and said neutral grey glass compositioncomprises 0.15-0.60 MnO₂ and 1.2-1.6 wt. % total iron as Fe₂ O₃.
 14. Aglazing for automotive or architectural use prepared from the neutralgrey glass composition of claim 1.